It is known that a power supply device obtains a direct current power supply based on an alternating current power supply as an input source and an alternating current input voltage detection circuit detects an alternating current input voltage (a voltage of the alternating current power supply) to thus output a voltage detection signal. FIG. 8 illustrates an example of the power supply device and the alternating current input voltage detection circuit of the background art. In FIG. 8, the power supply device 10 has a diode rectification circuit 2 and a smoothing capacitor 3. Also, the alternating current input voltage detection circuit 20 is provided in the power supply device 10.
The diode rectification circuit 2 includes four diodes D11 to D14 that forms a full-wave rectification circuit having a bridge configuration. One alternating current input terminal 2a of the diode rectification circuit 2 is connected to one terminal of an alternating current power supply 1 through an alternating current power supply line L1 and to a connection point of the diode D11 and the diode D12. The other alternating current input terminal 2b of the diode rectification circuit 2 is connected to the other terminal of the alternating current power supply 1 through an alternating current power supply line L2 and to a connection point of the diode D13 and the diode D14. Also, a positive direct current output terminal 2c of the diode rectification circuit 2 is connected to a connection point of the diode D11 and the diode D13 and to one end of the smoothing capacitor 3. A negative direct current output terminal 2d of the diode rectification circuit 2 is connected to a connection point of the diode D12 and the diode D14 and to the other end of the smoothing capacitor 3.
The other end of the smoothing capacitor 3 is grounded and thus becomes a reference potential of the power supply device 10. Also, the smoothing capacitor 3 is connected in parallel with a load 30.
The alternating current input voltage detection circuit 20 includes resistances R5 to R7 and a diode D15. One end of the resistance R5 is connected to the one terminal of the alternating current power supply 1 or one alternating current input terminal 2a of the diode rectification circuit 2, one end of the resistance R6 is connected to the other end of the alternating current power supply 1 or other alternating current input terminal 2b of the diode rectification circuit 2, the other end of the resistance R5 is connected to the other end of the resistance R6 and to an anode of the diode D15, a cathode of the diode D15 is connected to one end of the resistance R7 and the other end of the resistance R7 is grounded. Also, a connection point of the one end of the resistance R5 and the one terminal of the alternating current power supply 1 or a connection point of the one end of the resistance R5 and the one alternating current input terminal 2a of the diode rectification circuit 2 is referred to as a point A, a connection point of the one end of the resistance R6 and the other terminal of the alternating current power supply 1 or a connection point of the one end of the resistance R6 and the other alternating current input terminal 2b of the diode rectification circuit 2 is referred to as a point B, and a connection point of the cathode of the diode D15 and the one end of the resistance R7 is referred to as a point C.
In the below, operations of the power supply device 10 and alternating current input voltage detection circuit 20 configured as described above will be described.
The power supply device 10 full-wave rectifies an alternating current input voltage, which is supplied from the alternating current power supply 1, by the diode rectification circuit 2, smoothes the full-wave rectified voltage by the smoothing capacitor 3 to convert into a direct current output voltage and thus outputs the direct current output voltage to the load 30 that is connected in parallel with the smoothing capacitor 3. Also, a power supply device, in which the smoothing capacitor 3 is replaced with a power conversion unit (not shown) of a boost converter to has a function of improving a power factor of the alternating current power supply 1 and to output a direct current output voltage higher than the alternating current input voltage, and a power supply device, in which a power conversion unit (not shown) such as DC-DC converter and DC-AC converter is provided between the smoothing capacitor 3 (or boost converter) and the load 30 to convert the alternating current input voltage into a desired direct current output voltage or alternating current output voltage and to output the same, have been also known.
The alternating current input voltage detection circuit 20 is a circuit that detects the alternating current input voltage supplied from the alternating current power supply 1 and thus outputs a voltage detection signal, inputs voltage waveforms of the points A and B, on the basis of the reference potential (ground) of the power supply device 10, and outputs a voltage waveform of the point C as the voltage detection signal. The voltage detection signal is output from the alternating current input voltage detection circuit 20 is used to detect a voltage value such as average value and effective value of the alternating current input voltage and is used to detect a zero cross of the alternating current input voltage and to detect an abnormality (outage, voltage lowering, overvoltage and the like) of the alternating current power supply 1, at an inside or outside of the power supply device 10.
Also, for example, JP-A-11-155284 discloses an outage detection circuit, as a related technology of the background art.